Electrolysis cell with permeable valve metal anode and diaphragms on both the anode and cathode

ABSTRACT

DESCRIBES AN ELECTROLYSIS CELL, AND METHOD OF OPERATING THE CELL, HAVING PERMEABLE VALVE METAL ANODES (PREFERABLY TITANIUM OR TATALUM) AND PERMEABLE METAL CATHODES IN WAVE FORM, EACH WITH CLOSED ENDS AND EACH COVERED BY DIAPRAGMS, WITH THE WAVES OF THE CATHODE FINGERS LYING BETWEEN THE WAVES OF THE ANODE FINGERS TO PROVIDE A LARGE ELECTRODE AREA IN A SMALL CELL CONTAINER. THE ANODES AND CATHODES IN WAVE FORM ARE INTERMESHED TOGETHER AND THE CELL MAY BE UNIPOLAR, OR BIPOLAR WITH TERMINAL POSITIVE AND NEGATIVE END CELL UNITS AND A PLURALITY OF INTERMEDIATE CELL UNITS. THE ANOLYTE AND CATHOYLTE DISCHARGE MEANS ARE ADJUSTABLE IN ORDER TO CONTROL THE ANOLYTE AND CATHOLYTE LIQUOR LEVELS BEHIND EACH DIAPHRGM.

May 7, 1.74 Q DE NORA ETAL 3,809,630

' ELECTROLYSIS. CELL WITH PERMEABLE VALVE METAL ANODE AND' DIAPHRAGMS ONBOTH THE ANODE AND CATHODE Filed Feb. 17, 1972 7 Sheets-Sheet 1 ANOLYTEOVERF 4 F G 1 FEED BRINE QCATHOLYT OVERFLOW 0 DE NORA ETAL May 7,1974

ELECTROLYSIS CELL: WITH PERMEABLE VALVE METAL ANODE AND DIAPHRAGMS ONBQTH THE ANODE AND (.IATHODE Filed Feb. 17, 1972 '7 Sheets-Sheet FIG.2

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I DIAPHRAGMS ON BOTH THE ANODE AND CATHODE Filed Feb. 17, 1972 7Sheets-Sheet 3 ay 1,74 0. DE NORA E'II'AL 3,809,630 E VALVE} METAL ANODEAND ELECTROLYSIS CELL WITH PERMEABL DIAPHRAGMS ON BOTH THE ANODE ANDCATHODE Filed Feb. 17, 1972 7 Sheets-Sheet &

FIG.4

y 0. DE NORA ETAL 3,809,630 ELECTROLYSIS GEILL WITH FERMEABLE VALVEMETAL mom: AND

DIAPHRAGMS ON BOTH IHE ANODE ANT) CATHODE 7 Sheets-Sheet 5 Filed Feb.17. 1972 y 1974 0. DE NORA ETAL 3,809,

ELECTROLYSIS CELL WITH FERMEABLE VALVE METAL ANODE AND DIAPHRAGMS ONBOTH THE ANODE AND CATHODE '7 Sheets-Sheet 6 Filed Feb. 17, 1972 ANODETITANIUM CATHODE SCREEN WITH DlAPl-lRAGM Free ANOLYTE RINE FEED E NORAETAL 3,309,630 PERMEABLE VALVE METAL ANQDB AND May 7, 1974 ELECTROLYSISCELL w nmmmmms on BOTH THE mom: AND cmxomz Filed Feb. 17, 1972 1 '7Sheets-Sheet "FIG.7

United States Patent ELECTROLYSIS CELL WITH PERMEABLE VALVE METAL ANODEAND DIAPHRAGMS ON BOTH THE ANODE AND CATHODE Oronzio de Nora, Milan,Italy, and Vittorio de Nora, Nassau, Bahama Islands, assignors toOronzio de Nora Impianti Elettrochimici S.p.A., Milan, ItalyContinuation-impart of application Ser. No. 51,162,

June 20, 1970. This application Feb. 17, 1972,

Ser. No. 227,116 Claims priority, application Italy, Oct. 19, 1971,30,038/71 Int. Cl. C01d 1/06 US. Cl. 204-98 18 Claims ABSTRACT OF THEDISCLOSURE Describes an electrolysis cell, and method of operating thecell, having permeable valve metal anodes (preferably titanium ortantalum) and permeable metal cathodes in wave form, each with closedends and each covered by diaphragms, with the waves of the cathodefingers lying between the waves of the anode fingers to provide a largeelectrode area in a small cell container. The anodes and cathodes inwave form are intermeshed together and the cell may be unipolar, orbipolar with terminal positive and negative end cell units and aplurality of intermediate cell units. The anolyte and cathoyltedischarge means are adjustable in order to control the anolyte andcatholyte liquor levels behind each diaphragm.

This application is a continuation-in-part of our copending applicationSer. No. 51,162, filed June 20, 1970.

This invention relates to electrolysis cells having dimensionally stablevalve metal anodes and cathodes which are permeable to electrolyte flowtherethrough and in which both the anodes and cathodes are provided withpermeable diaphragms of asbestos or similar material through which theelectrolyte can flow.

Permeable cathodes, consisting of cathode screens covered withdiaphragms have long been used in electrolysis cells to separate thecathode gases and liquids from the electrolyte. For example, in theelectrolysis of sodium chloride in diaphragm cells to produce chlorineand caustic soda, chlorine is released at the anodes and is recoveredfrom the anode compartments and sodium is released at the cathodes andforms sodium hydroxide and hydrogen in the cathode comparements, thehydrogen gas, sodium hydroxide (approximately 11-12% strength) anddepleted brine are recovered from the cathode compartments. Thisinvention also uses diaphragms over permeable valve metal anodes so thatbrine from the electrolyte inlet compartment can be flowed through boththe diaphragm covered permeable anodes and the diaphragm coveredcathodes and difierent gas and/ or liquid products recovered from boththe anode and cathode compartments.

This invention will be described with reference to the production ofchlorine and caustic soda from sodium chloride brine, but it is to beunderstood this is only for purposes of illustration and that theinventions herein described may be used for the electrolysis of otheralkali halides, for the electrolysis of sodium and potassium sulfates toproduce caustic soda or caustic potash, sulfuric acid and oxygen,forelectro-osmosis and electrodialysis, for organic oxidation andreduction reactions, for electrometallurgical uses and for otherprocesses which may be carried out by electrolysis reactions in the celland process herein described.

The electrodes may be either unipolar or bipolar as will be described,provided both the anodes and cathodes are permeaable and at least one iscovered with a diaphragm.

One of the objects of this invention is to provide new types ofpermeable anodes and cathodes, each covered with h diaphragm in whichthe diaphragm covered anodes and cgathodes are in wave or finger formwith the cathode waves lying between the anode waves so that electrolytecan be flowed into the interelectrodic gap between the anode and cathodesurfaces and flowed through the cathode diaphragm to the catholytecompartment and through the anode diaphragm to the anolyte compartment,the cathodic products being released in the catholyte compartment andthe anodic products being released in the anolyte compartment.

Another object of the invention is to provide an apparatus and processin which the liquid level in each of the electrolyte, anolyte andcatholyte compartments can be controlled to give the desired flow ratethrough each of the anode and cathode diaphragms.

Various other objects and advantages of this invention will appear asthis description proceeds.

Referring now to the drawings, which show various concrete anddiagrammatic embodiments of the invention for the purpose ofillustration:

FIG. 1 is a plan view with parts broken away, and parts shown in dashlines of a three unit bipolar cell constructed according to theprinciples of this invention;

FIG. 2 is a part. sectional side view, with parts broken away and partsshown in dash lines, of the cell illustrated in FIG. 1;

FIG. 3 is a partial front view of the three unit bipolar cellillustrated in FIGS. 1 and 2, also with parts shown in dash lines;

FIG. 4 is a cross sectional view, approximately on the line 4--4 of FIG.1;

FIGS. 5 and 6 are detail cross sectional plan views of the anode-cathodeconnections in a bipolar cell;

FIG. 7 is an enlarged sectional plan view similar to FIGS. 5 and 6,showing the diaphragms on both the anode and cathode fingers with theelectrolyte being fed into the cell bet-ween the two diaphragms;

FIG. 8 is a digarammatic perspective view of a portion of another formof bipolar anode and cathode showing the connection therebetween; and

FIG. 9 is a perspective illustration of one form of open titanium meshsuitable for use in the cells of this invention.

In the cells hereinafter described, the anodes are constructed of avalve metal (titanium, tantalum, zirconium, tungsten or the like) whichis resistant to the corrosive conditions of an electrolysis cell andwhich will pass current in the cathode direction but will not passcurrent in the anode direction, hence the name valve metal. The valvemetals used in these cells are provided with an electrically conductingelectrocatalytic coating of a platinum group metal or mixed oxides ofvalve metals and platinum group metal oxides, or other electricallyconducting electrocatalytic coatings. The platinum group metals areplatinum, palladium, osmium, iridium and ruthenium. The preferred valvemetal is titanium provided with a coating of a mixed oxide of titaniumand ruthenium. However, other valve metals and other electrocatalyticcoatings may be used.

The anodes may be formed of titanium screen, perforated titanium sheets,slitted, reticulated titanium plates, titanium mesh, rolled titaniummesh, woven titanium wire or screen, titanium rods, or similar tantalumor other valve metal plates and shapes, or alloys of titanium or othervalve metals, all of which forms will be referred to herein as titaniummesh, and normally have from 30 to 60% (preferably 50 to 53%) ofopenings therethrough so that when covered by diaphragms the electrolytecan readily flow through these anodes.

Referring now to the embodiments of this invention illustrated in FIGS.1 to 7 of the drawings, FIG. I illustrates a three unit bipolar cellhaving a terminal positive end unit A, an intermediate unit B and aterminal nega-i tive end unit C. Only one intermediate unit B has beenillustrated, but it will be understood that any number of intermediateunits B, B, etc., may be used. The unit A consists of a positive (anode)end plate 1, preferably of steel, to which the positive electricalconnections 2 are secured. The plate 1 is provided with a titanium,tantalum or other valve metal lining 3 which is resistant to theelectrolyte and the electrolysis conditions encountered in the cell andtitanium mesh anode waves or fingers 4 with closed ends are connected tothe titanium lining by titanium connectors S, illustrated in greaterdetail in FIGS. 5 and 6 and described in detail below, which insure goodelectrical connections between the end plate 1 and the anode waves orfingers 4. The titanium or other valve metal lining 3 is secured to theend plate 1 by sandwich welding, using intermediate sandwich metals ifnecessary, or by bolting or any other connection which insures a goodmetal to metal electrical contact between the end plates 1 and theelectrolyte resistant lining 3. Titanium, tantalum or other valve metalsor alloys of these metals may be used for the lining 3 and the anodewaves or ringers 4.

The anode waves 4 are formed from open mesh titanium, tantalum or othervalve metal as diagrammatically illustrated in FIG. 9, and arecompletely covered with a diaphragm usually of asbestos fiber depositedunder vacuum on the open mesh anode structure, or of woven asbestoscloth. Before application of the diaphragms, the titanium or other valvemetal anodes are given an electrically conducting electrocatalyticcoating of a platinum group metal or a mixture of oxides of a valvemetal and a platinum group metal. The mixed oxide coating may be appliedas a solution of the desired ingredients and applied as a paint, sprayor the like and baked on the anodes. Usually multiple coats are appliedand baked in air at about 350 to 450 C. between each coat to deposit thematerials in solution and to oxidize the materials to the correspondingoxides of valve metals and platinum group metals. The coatings may beapplied to the front (facing cathode) or back of the anodes or to boththe front and back, or may be applied to only a portion of the anodefaces.

,The entire surface of the coated anodes facing the cathodes is coveredby diaphragms, not shown in FIGS. 1 and 2, but indicated by 4a in theFIGS. 5, 6 and 7.

The end anode plate 1 is spaced from a steel cathode supportin end plate1a, from which the steel screen cathode waves or fingers are supportedby welded strips or projections 7 which form the electrical connectionbetween the cathode fingers and the steel plate 1a. Each cathodesupporting end plate 1a (except the negative terminal end plate) isprovided on the anodic side, with a valve metal lining 3 as shown inFIGS. 1, 5 and 6 to form a bimetallic partition between each of thebipolar cell units. A spacer 8 forming the side walls of each cell unit,extends between the lining 3 and a squared pipe 9 which surrounds thecatholyte compartment 10 formed between the inside of the cathodefingers 6 and the plate 1a. The spacers 8 are lined with a titaniumlining 8a or other valve metal or electrolyte resistant lining which isresistant to the anolyte and the corrosive conditions encountered in anelectrolytic cell, and the end anode waves 4 are connected to the lining8a as indicated at 412 (FIGS. 1, 5 and 7). Alternatively, the end anodewaves 4 may project into the space between the flanges 8c of the spacers8 and the gaskets 11. Rubber gaskets 11 seal the joints between theplates 1 and 1a and the flanges 8c of the spacers 8 so that afluid-tight box-like structure housing the anode waves 4 and the cathodewaves 6 is formed between the plates 1 and 1a in each of units A, B andC of the bipolar cell. Inside each "cathode finger 6, zigzag bent steelreinforcements 12 are welded at spaced intervals to prevent collapse ofthe screen cathode waves or fingers 6 when an asbestos or otherdiaphragm material is deposited on the screen cathode fingers undervacuum. Similar reinforcements (not shown) may .be provided on theinside of the anode Waves away from the cathodes to prevent collapse ofthe mesh anode waves when diaphragm material is applied thereto.Thesteel screen cathode waves or fingers 6 are closed at the top andbottom as illustrated in FIG. 4 and are covered with a diaphragmmaterial 6a (FIGS. 5 and 6), usually either woven asbestos fiber orasbestos flock applied under vacuum.

The diaphragm material covers the side walls as well as the top andbottom of cathode waves or fingers 6. The titanium mesh anode waves 4between each cathode wave 6 are likewise closed at the top and bottom asindicated at 40 on the end anode and on the one intermediate anode 4shown in FIG. 4, to prevent the electrolyte from entering the anolytecompartments behind the diaphragm covering on the anodes 4. Only one endanode wave and one intermediate anode wave 4 has been shown in FIG. 4,but it will be understood that there are anode waves between eachcathode wave as illustrated in FIG. 4. The diaphragms on the anode andcathode waves are only partially and diagrammatically shown in FIGS. 5and 6, but it will be understood that both the anode and cathode wavesare completely covered with diaphragms when in use in the cells. Thediaphragms separate the anolyte compartments D and the catholytecompartments E from the electrolyte or brine compartment orinterelectrodic gap F (FIGS. 5, 6 and 7) and keep the gases and liquidsin each of these compartments separate.

The brine or electrolyte is fed into the interelectrodic gap F betweenthe anodes and cathodes and flow through the diaphragms 4a and 6a intothe anolyte compartments D and catholyte compartments E and the gasesand liquids in the anolyte and catholyte compartments are separatelyrecovered as described below.

When the cell illustrated in FIGS. 1 to 3 is in use, the electrolyzingcurrent flows through the electrolyte in the interelectrodic gap F fromthe anode waves 4 to the oathode waves 6. Anodic gases are released atthe anode waves or fingers 4, behind the diaphragms 4a, the electrolyteor brine flows through the diaphragms surrounding both the anode waves 4and cathode waves 6 and the cathodic gases and liquids formed at thecathode surfaces inside the diaphragms are discharged from the cathodiccompartments through the outlets 17 and 18. The anodic gases and liquidsare discharged through the outlets 13 and 40.

When used for the production of chlorine and caustic soda from sodiumchloride brine, chlorine (or other anodic gases) released at the anodes4 rises through the anolyte and escapes through the chlorine outlet 13to the chlorine recovery system. Saturated brine flows from brinecontainer 14 through pipe connections 16 and feed branches 16b shown indash lines in FIG. 3 into the space between the anodes 4 and cathodes 6.The feed brine is fed into the lowest part of spaces F between thediaphragm covered anode and cathode fingers of the cell units A, B andC, so that the flow of saturated brine in the interelectrodic gap isfrom the bottom upward.

Brine is fed continuously or as needed from the saturated brine systeminto the brine containers 14 and a sight glass 16a (FIG. 3) indicatesthe level of the brine in the brine container 14. The space between theanodes and cathodes is continuous from side 8 to side 8 of each cellunit as illustrated in FIGS. 1, 2, 5, 6 and 7, so that the saturatedbrine flows into the interelectrodic gap F between the anodes 4 andcathodes 6 and completely fills this space.

The brine containers 14 provide a hydrostatic pressure head ofelectrolyte in space F of each electrolyzer.

Sodium hydroxide and hydrogen released at the cathode fingers flows intothe catholyte space E behind the cathode diaphragms surrounding thecathode fingers 6 and the end plates 1a and into a squared pipe 9 (FIG.4) which surrounds the catholyte space. The hydrogen flows upwardthrough the holes 9a at the top of the squared pipe 9 and out throughthe hydrogen outlets 17 and the depleted brine containing the sodiumhydroxide (about 11-12%) flows through the holes 9b to the catholyteoutlet 18. The squared pipes 9 communicate only with the catholytecompartment E as shown in FIGS. 1 and 2. An electrolyte drain 18a nearthe bottom of the square pipe 9 permits the catholyte compartment, aswell as the anolyte compartment and the interelectrodic gap space ofeach cell unit, to be drained. Partitions 18b at each end of the bottomleg of squared pipe 9 seal off the bottom leg, so that no electrolyteenters the bottom leg of squared pipe 9. A telescoping pipe connection180 (FIG. 3) communicating with the catholyte outlet 18 is adjustable tocontrol the level of the catholyte in the catholyte compartments B, sothat the catholyte level is always sufiiciently below the electrolytelevel in space F to insure a sufiicient flow from the electrolytecompartments or interelectrodic gap space F through the diaphragms intothe catholyte compartments E. In a similar way, a telescoping tubeconnection 18d maintains the level of the anolyte in the anolytecompartments D sufliciently below the level of the brine in theinterelectrodic gap to insure fiow through the anode diaphragms 4a. Thetelescoping drain pipes 180 and 18d are of the same construction andeach can be adjusted by moving the upper section 18e upwardly on thelower section 18 to adjust the overflow height 18g, so that the level ofthe anolyte or catholyte in the compartment D or E is below the level ofthe brine in the gap F. A hollow tube 18h connected to the upper section18e permits this adjustment and serves to break any syphon effect in thetelescoping drain pipes 18c and 18d. In place of the telescoping pipes,the usual inverted U-shaped perk tube may be used to control the anolyteand catholyte level in the compartments D and E.

The cell units A, B, B, B and C are mounted on I-beam supports 19 (FIG.3), supported on insulators 19a. Syenite plates 20 cemented to the upperfaces of the I-beams 19 insulate the titanium lined boxes of the cellunits A, B and C from the metal I-beams and permit the heavy elements ofthe cell units to slide on the syenite plates 20 without too greatfriction during assembly or disassembly of the units. The sides 8 andthe ends 1 and 1a are held together by tie rods 21a, suitably insulatedfrom their surrounding parts by means of insulating bushings, as shownin FIGS. 1 and 5. The temporary bolts 21 shown in FIG. 5 are used onlyduring assembly of the electrolyzer, to tighten the units together andare taken off before start up of the cell in order to avoid shortcircuits. During operation of the cell, the tie rods 2.1a, suitablyinsulated from their surrounding parts, hold the terminal end plates 1and 1a and the side spacers 8, forming the electrolyte box of each cellunit, together. The tie rods 21a extend from the positive terminal endplate 1 of unit A to the negative terminal end plate 1a of the terminalunit C, regardless of the number of intermediate units B in the bipolarcell assembly.

The electrolyzing current flows consecutively from the positive terminal2 through the end unit A, through the intermediate units B, which varyin number from one to twenty or more, depending on the size and use ofthe bipolar cell, and through the terminal unit C to the negativeterminal 2a of the circuit. The diaphragm covered anode waves or fingers4 are preferably made of titanium mesh, suitably coated with anelectrocatalytic conductive coating such as a platinum group metal ormixed oxides of titanium and platinum group metal oxides. Other valvemetals and other coatings may be used. The cathode waves or fingers 6are preferably steel screen material or other ferrous metal similar tothe cathode screens now used in diaphragm cells. However, other metalsmay be used for the anode and cathode waves depending on the material tobe electrolyzed and the end products to be produced.

The anodes 4 and cathodes 6 are preferably formed as uniform waves orfingers nested together and uniformly spaced apart, as illustrated inFIGS. 1, 5, 6 and 7, to provide a substantially uniform electrode gapbetween the anodic surfaces and the cathodic surfaces. During as sembly,the anode waves 4 and cathode waves 6 may be moved together by movingthe plates 1 and 1a with the anodes and cathodes mounted thereonhorizontally toward each other, to form the nesting anode and cathodewaves as illustrated in FIGS. 1, 2, 5, 6 and 7, or, by giving a slighttaper in the vertical direction to the anode and cathode waves, theanodes and cathodes may be nested together by vertically inserting thecathode waves between the anode waves. The anode waves 4 and cathodewaves 6 need not be as long or deep as illustrated. Shallower waves maybe used, but the deeper waves illustrated provide greater anode andcathode surfaces Within cell units of the same square area thanshallower waves would provide. Flat planar anodes and cathodes could beused but would not provide as large area as the wave form.

The words waves or fingers wherever used in the specification or claimsare intended to describe the wave embodiments of FIGS. 1 to 7 or thefinger embodiment of FIG. 8.

To insure good electrical connection between the anodic and the cathodicsections of the cell, the anodic metals, such as titanium, tantalum andother valve metals, are preferably sandwich welded to the steel plates 1and 1a constituting the anodic and cathodic pole of any single cellunit, using appropriate intermediate metals, such as copper, lead,silver, zinc, etc., to form the sandwich weld, if necessary. Other meanswhich will provide good electrical connections may be used.

As illustrated in FIG. 5, the anodes waves 4 are connected to thetitanium lining plate 3 by titanium or other cylinders 5 welded to theplate 3. The cylinders 5 are screw threaded on the inside and titaniumbolts 5a (FIG. 6) are used to connect the anodes waves 4 to thecylinders 5 and plate 3, using titanium strips 22b, where the titani: umanodes are welded on. The steel cathode waves 6 are connected to theplates 1a by steel strips 7 welded to the plates 1a and to the trough ofthe waves 6 The anode and cathode waves are entirely covered with adiaphragm material, such as woven asbestos, ashestos fibers or the like,partialy illustrated at 4a and 6a in FIGS. 5, 6 and 7. A modified formof connection between the steel plates 1a and the anode waves isillustrated in FIG. 6, in which holes 22 are drilled part-way throughplates 1a and screw threaded. Hollow titanium bolts 22a are screwed intothese holes and, after tightening, are welded to the titanium plate 3 toinsure a fluid tight connection, and titanium bolts 5a are used toconnect the titanium strips with the trough of anode waves 4 and withthe hollow titanium bolts 22a. Titanium strips 22b distribute thecurrent to the anode waves 4. The titanium anode waves 4 may be solidtitanium sheet, perforated titanium sheet, slitted, reticulated titaniumplates, titanium mesh, rolled titanium mesh, woven titanium wire orscreen, horizontally or vertically arranged titanium rods or bars orsimilar tantalum and other valve metal plates and shapes or alloys oftitanium or other valve metals, or any other conductive form of titaniumand the waves 4 are provided with a conductive electrocatalytic coatingcapable of preventing the titanium from becoming passivated, and whenused for chlorine production are capable of catalyzing discharge ofchloride ions from the surfaces of the anodes. The coating may be oneither one or both faces of the anode waves and is preferably on theface of the anode waves 4 facing the cathodes 6.

The diaphragms on the anode waves 4 and the cathode waves 6 keep theanolyte liquor and catholyte liquor separated by cell liquor in theinterelectrodic gap F between the diaphragms. The brine or electrolyteundergoing electrolysis is flowed into the space F between the anodediaphragms and the cathode diaphragms and the anolyte liquor and gaseousanode products flowed out from the outside of the anode fingers orwaves, as the gaseous and liquid cathode products are flowed out fromthe outside of the cathode fingers in the embodiments of FIGS. 1 to 7described above.

It is also possible to use a diaphragm only on the anodes 4, in whichevent the anolyte gases and liquids are separated from the catholytegases and liquids only by the diaphragms 4a.

In the diagrammatic illustration of FIG. 8, the perforated orreticulated titanium anode waves or fingers 30 are mounted in the frontof a titanium hollow box 31 with which the hollow insides of the fingers30 communicate. The back of the box 31 is a sheet of titanium 31a whichis welded, bolted or otherwise secured to the back 32a of the steel box32 to which the screen cathode fingers 33 are secured. The interior ofthe diaphragm covered cathode fingers communicates with the interior ofsteel box 32 and the interior of the diaphragm covered anode fingerscommunicates with the interior of the titanium box 31. Eachanode-cathode assembly illustrated in FIG. 8 is enclosed in asurrounding box or frame (not shown) similar to the box or frame 8 inFIG. 1. While only two anode fingers 30 and one cathode finger 33 areshown in FIG. 8, it will be understood that a plurality of anode andcathode fingers are used and that these fingers mesh as illustrated inFIGS. 1, 5, 6 and 7. In a complete cell according to FIG. 8, the anodeand cathode fingers are meshed together to form intermediate cell unitsand terminal positive and negative end plates are provided to form abipolar cell containing the anode and cathode sets illustrated in FIG.8.

Brine enters the space between the anode and cathode fingers at brineinlet 38 diagrammatically illustrated in FIG. 8 and flows out throughthe diaphragm covered anode fingers 30 and through the nested diaphragmcovered cathode fingers 33 (not shown), facing the anode fingers 30 atthe left side of FIG. 8. The brine feed lines 38 are preferably locatedunder the anode and cathode fingers and feed brine into theinterelectrodic gap between the diaphragms on the anode and cathodefingers. Chlorine formed at the anodes flows out box 31 at the chlorineoutlet 35 and the depleted brine fiows from the outlet 34 through atelescoping tube similar to 180 previously described, which controls theanolyte level in the anolyte compartments. Hydrogen released inside thediaphragms at the cathode fingers 33 flows out of outlet 36 and sodiumhydroxide 1l-12%) and depleted brine flow from the outlet 37, alsoprovided with a telescoping tube to control the catholyte level in box32.

The compartments housing the anodes 30 are preferably titanium lined asdescribed in connection with FIGS. 1 and 5, and the anodes are titaniumprovided with an electrically conducting electrocatalytic coating.

FIG. 9 shows one form of open mesh titanium anode screen 44 havingapproximately 50 to 53% voids or openings 45, therein. The anodes may beany form of titanium or other valve metal screen mesh or rods and areapproximately 34, to 1 inch in thickness and may be bent to the desiredshape or form before or after the electrically conductingelectrocatalytic coating is applied thereto.

One coating procedure which may be used on the anodes ,4 and 30 is asfollows:

The anodes are cleaned by boiling at reflux temperature of 110 C. in a20% solution of hydrochloric acid for 40 minutes and are then dried andcoated as follows:

Titanium trichloride in HCl solution is dissolved in methanol, the TiClis converted to the pertitanate by the addition of H 0 This conversionis indicated by a change in color from TiCl (purple) to Ti O (orange).An excess of H 0 is used to insure complete conversion to thepertitanate. Sufiicient RuCl -3H O is dissolved in methanol to give thedesired final ratio of TiO to RuO The solution of pertitanic acid andruthenium trichloride are mixed and the resulting solution is applied toone or both sides of a cleaned titanium anode surface by brushing,spraying or the like. The coating is applied as a series of coats withbaking at about 350 C. for five minutes betweeneach coat. After acoating of the desired thickness or weight per unit of area has beenapplied, the deposit is given a final heat treatment at about 450 C. forfifteen minutes to one hour. The molar ratio of TiO to RuO may vary from1:1 TiO :RuO to 10:1 TiO :RuO The molar values correspond to 22.3247Weight percent TizRu and 51:10.8 weight percent TizRu.

Anodes produced in this way have high conductivity and electrooatalyticactivity in chlorine cells which continue without material diminutionover a long period of time.

The thickness of the coating may be varied according to theelectrochemical needs. A typical coating to give 46 mg. Ru metal and mg.titanium in the oxide coating for every 6 sq. in. of anode surface maybe prepared by using 117.9 mg. RuCl -3H O (39% Ru metal) and 80 mg. oftitanium metal as TiCl (80 mg. Ti dissolved in dilute 'HCl sufiicientlyin excess to maintain acidic conditions). Methanol is added to thetitanium trichloride solution and the solution is oxidized with H 0 toproduce the pertitanate. The resulting solution is painted on a titaniumanode substrate in multiple coats with drying or baking at 350 C. forfive minutes between each coat. Five to fifteen coats may be required. Afinal heat treatment at 450 C. for one hour is given to complete thecoating. The molar ratio of Ti to Ru or TiO to R in the above coatingsis 3.65:1.

In place of ruthenium, any platinum group metal may be used and in placeof titanium, tantalum or other valve metals or alloys may be used in thecoating formulation. If a platinum group metal coating is used on theanode mesh surfaces, it may be applied by electro-deposition orchemi-deposition.

Valve metal anodes coated as described have the prop erty of convertingchloride ions (anions) discharged at the anode to chlorine moleculesaccording to the reaction The chlorine molecules, as bubbles, rise alongthe back of the anodes or are swept off the anodes by the flow ofelectrolyte through the diaphragms and rise in the anolyte compartmentsD to the top of the cell units and escape through C1 passages 13 to thechlorine recovery system.

The concrete and diagrammatic embodiments of the invention shown hereinare for illustrative purposes only and various modifications and changesmay be made within the spirit and objects of the invention. The cellsillustrated may be used as unipolar single cells or as bipolar multiplecells and white titanium and steel have been described as the metals ofconstruction, various dissimilar metals may be used for the anodes andcathodes of the cell units. Examples of other suitable anode metals arelead, silver and alloys thereof and metals which contain or are coatedwith PbOg, MnO Fe O etc., and examples of other suitable cathode metalsare copper, silver, stainless steel, etc. The metals used should besuitable to resist the corrosive or other conditions encountered in thecell when operating on a particular electrolyte.

What is claimed is:

1. The method of carrying out an electrolysis reaction in anelectrolytic cell having an anolyte compartment, a catholytecompartment, a permeable anode in said anolyte compartment, a permeablecathode in said catholyte compartment, diaphragms covering each of theanodes and cathodes, means to feed an electrolyte into theinterelectrodic gap between the diaphragms on the anodes and cathodes,means to impress an electrolysis current across said gap, means towithdraw anodic gases from the anolyte compartment and adjustable meansto withdraw anolyte liquor from the anolyte compartment, adjustablemeans to withdraw cathodic gases and liquids from the catholytecompartment, which comprises coating the anode with an electricallyconductive electrocatalytic coating, covering the anodes and cathodeswith diaphragms and passing an electric current through theinterelectrodic gap to decompose the electrolyte, catalyzing theformation of anions to gas bubbles on the anode, sweeping the gasbubbles off the anode by the flow of electrolyte through the anodediaphragm and anode, recovering the anodic and cathodic products fromthe anolyte and catholyte compartments and maintaining the anolyte andcatholyte level in the anolyte and catholyte compartments below theelectrolyte level in the interelectrodic gap by adjusting saidadjustable anolyte and catholyte withdrawal means.

a 2. The method of claim 1, in which the permeable anode is a valvemetal and the electrically conductive electrocatalytic coating containsa material from the group consisting of platinum group metals andcompounds of platinum group metals.

3. The method of claim 1, in which the permeable anode is titanium andthe electrically conductive electrocatalytic coating comprises a mixtureof a valve metal oxide and a platinum group metal oxide.

4. In an electrolysis cell unit, a plurality of permeable metal anodesin wave form, a plurality of permeable metal cathodes in wave form, thesaid anodes and cathodes extending substantially from the bottom to thetop of said cell unit and being nested together to provide asubstantially uniform spacing between the anode and cathode surfaces, avalve metal support for said anodes, a ferrous metal support for saidcathodes and means to connect said anodes and cathodes in electricalconnec- 3 tion to said supports and means to conduct electrolysiscurrent to and from said supports, a diaphragm on said anode waves, adiaphragm on said cathode waves, said diaphragms facing each other,means to feed an electrolyte to the space between said diaphragms insaid cell, means to pass an electrolysis current through the electrolytebetween said anode and cathode surfaces, means to discharge anodic gasesfrom said cell behind the anode diaphragms, means to discharge thecathodic gases from said cell behind the cathode diaphragms, means todischarge anolyte liquor from said cell behind the anode diaphragms,means to discharge catholyte liquor from said cell behind the cathodediaphragms, both said anolyte liquor and catholyte liquor dischargemeans being adjustable to control the anolyte and catholyte liquor levelbehind said diaphragms.

5. The cell of claim 4, in which the anodes are made of titanium and theelectrocatalytic coating contains a material from the group consistingof platinum group metals and oxides of platinum group metals.

6. The cell of claim 4, in which a plurality of said cell units arecombined into a bipolar electrolysis cell, a continuous bimetallicpartition of ferrous metal on the cathode side and a valve metal on theanode side is provided between each cell unit, separating the cathodesand anodes and means are provided to connect the cathodes and the anodesin electrical connection to said partitions.

7. A bipolar electrolyzer according to claim 6, in which a container onthe top of each cell unit feeds fresh brine into the cell units betweenthe anode diaphragms and the cathode diaphragms.

8. A bipolar electrolysis cell according to claim 6, in which thecathodes are diaphragm covered steel net and the anodes are titaniummesh provided with a conductive electrocatalytic coating covered bydiaphragms.

9. A bipolar electrolysis cell according to claim 8, in which the anodesare in the form of fingers extending from a titanium supporting backplate, the cathodes are in the form of fingers extending from a steelsupporting back plate, the anode fingers and the cathode fingers nesttogether providing a uniform spacing therebetween and the titanium backplate and the steel back plate are secured together to provide ametallic bipolar electrical contact between one cell unit and theadjacent cell unit.

10. A bipolar electrolyzer according to claim 9, in which the cathodicsteel back plate is surrounded by a rectangular-shaped steel pipe frame,said frame has a number of holes in its upper horizontal leg for thepassage of gas into the horizontal leg and a gas discharge passage fromsaid horizontal leg and one of the side legs of said frame has holes forthe passage of catholyte liquor into said side leg and an adjustablecatholyte liquor outlet is connected to said side leg.

11. A bipolar electrolysis cell according to claim 9, in which the anodeand cathode fingers are formed with closed upper and lower ends.

12. In a bipolar electrolysis cell, a positive end unit containinganodes and cathodes, a negative end unit containing anodes and cathodesand a plurality of intermediate units containing anodes and cathodes,all of said units being connected in series to pass a electrolysiscurrent through all of said cell units, the anodes and cathodes beingconstructed of permeable metal in the form of finger-like waves whichare nested together, a bimetallic separating partition between the cellunits, the cathodes of one cell unit being connected to the anodes ofthe adjacent cell unit by a metal to metal contact through said cellunits, diaphragms covering each of said anodes and cathodes, means tofeed an electrolyte to the space between said diaphragms, adjustablemeans to discharge anolyte liquor from each of said cell units behindthe anode and diaphragms and adjustable means to discharge catholyteliquor from each of said cell units behind the cathode diaphragms.

13. The electrolysis cell of claim 12, in which the anodes are formed oftitanium mesh having an electrocatalytic conductive coating thereon andthe cathodes are formed of ferrous metal screens.

14. The cell of claim 12, in which the anodes are supported on atitanium back plate, the cathodes are supported on a ferrous metal backplate and the two back plates are secured together with a metal to metalcontact.

15. The cell of claim 14, in which the space between the cathodes andthe cathode back plate forms a catholyte chamber and said space issurrounded by a rectangular pipe, said pipe having openings to receiveand discharge catholyte gas and openings to receive and dischargecatholyte liquor and the space between the anodes and the anode backplate forms an anolyte chamber and means to discharge anodic gases andanolyte liquor from said anolyte chamber.

16. In an electrolysis cell, a first hollow metal box-like support,metal anode fingers supported on and projecting from said first box-likesupport, diaphragms covering said anode fingers, a second hollow metalbox-like support, cathode fingers supported on and projecting from saidsecond box-like support, diaphragms covering said cathode fingers, thesaid first and second box-like supports being secured together, back toback, in electronically conductive contact, means to feed electrolyte tothe space between said diaphragms, adjustable means to discharge anolyteliquor from the first hollow box-like support and adjustable means todischage catholyte liquor from the second box-like support.

17. The cell of claim 16, in which the first hollow boxlike support andthe anode fingers supported thereby are made of titanium and the anodefingers have an electrically conducting electrocatalytic coatingthereon, the second hollow box-like support and the cathode supportedthereby are made of steel.

18. In an electrolysis cell, a plurality of cell units, a rectangularframe around each cell unit, an anode compartment and a cathodecompartment in each cell unit, said anode compartments and cathodecompartments being separated from the anode and cathode compart ments ofthe adjacent cell units by a continuous bimetallic separating partitionof a ferrous metal on the cathode side and a valve metal on the anodeside, said frames and the anode and cathode compartments therein beingsubstantially rectangular throughout and extending substantially fromtop to bottom and from side to side of said cell units, a plurality ofvalve metal anodes in hollow wave form in each said anode compartment,valve metal electrical connectors between the base of the waves of saidanodes and the valve metal of said bimetallic separating partition, saidelectrical connectors spacing the anodes from the valve metal of saidpartitions, an electrically conductive electrocatalytic coating on saidanode waves, a plurality of metal cathodes in wave form in said cathodecompartments, electrical connectors between the base of said cathodewaves and the ferrous metal of said bimetallic partitions, saidelectrical connectors spacing the cathodes from the ferrous metal ofsaid partitions, said anodes and cathodes extending substantiallyvertically in said compartments substantially from the top to the bottomand from side to side of said compartments, said anodes and cathodesbeing nested together to provide a substantially uniform spacing betweenthe anode and cathode surfaces, said anodes and cathodes being of openmesh construction, a diaphragm adjacent the anodes, a separate diaphragmadjacent the cathodes, both said diaphragms being between the anodes andcathodes, a lining on the side walls of said anode compartmentsresistant to the electrolyte and electrolysis conditions, means to feedan electrolyte to said cell between said diaphragms, means to pass'anelectrolysis current through the electrolyte between said anode andcathode surfaces, means to dis charge anodic gases and cathodic gasesfrom said cell, and adjustable means to discharge a catholyte liquorfrom the cathode compartments of said cell units and adjustable means todischarge anolyte liquor from the anolyte compartments of said cellunits.

References Cited 1 UNITED De Nora 204129 JOHN H. .MACK, Primary ExaminerW. LSOLOMON, Assistant Examiner US. Cl. X.R.

